The present invention relates to an electromagnetic-induction coupling device capable of forming a stable internal power source from power energy supplied from an external apparatus by electromagnetic-induction coupling by means of a coil and/or capable of stable information communication with the external apparatus through the coil.
A ball semiconductor has recently been proposed in which function elements, such as transistors, sensors, etc. and a semiconductor integrated circuit that has given processing functions are formed on the surface of a ball semiconductor chip with a diameter of about 1 mm. Some ball semiconductors of this type are provided with a coil (loop antenna) 2 that is formed on the surface of a ball semiconductor chip 1 and serves as an antenna element, as shown in FIG. 4, for example. These ball semiconductors are constructed so that they are actuated with power supplied from an external apparatus by utilizing electromagnetic-induction coupling by means of the coil 2, and transmit to and receive information signals from the external apparatus through the coil.
The integrated circuit formed on the semiconductor chip 1 comprises a power source unit 3, a reception unit 4, and a transmission unit 5, as shown in FIG. 5, for example. The power source unit 3 receives power (electromagnetic energy) externally supplied through the coil 2 and forms a fixed internal power source. The reception unit 4 receives the information signals from the external apparatus through the coil 2. The transmission unit 5 transmits the information signals to the external apparatus through the coil 2. Further, the integrated circuit comprises a device body 6, which is formed of an arithmetic and control element or the like, a sensor element 7 such as a temperature sensing element, a memory 8, etc., and is constructed so as to fulfill its given function as the device body 6 is actuated.
The information signals are transmitted and received through the coil 2 in a manner such that the information signals are modulated with use of an electromagnetic-induction magnetic field for power transmission as a carrier.
As shown in FIG. 6, for example, the power source unit 3 comprises a rectifier 3a that subjects power energy supplied through the coil 2 to full-wave rectification. In general, the rectifier 3a is constructed so that MOS transistors formed on the semiconductor chip 1 are bridge-connected. The power energy supplied through the coil 2 considerably changes depending on the distance from the external apparatus as a source of the energy, and is substantially in inverse proportion to the square of the distance. In a power supply system constructed so that necessary electromagnetic energy can be supplied to the ball semiconductor at a maximum distance Lmax, therefore, power that is four times as high as the power required by the ball semiconductor can be supplied if the distance between the ball semiconductor and the external apparatus is halved. In consequence, voltage (full-wave rectified output) that is obtained through the rectifier 3a has a quadruple voltage value if the internal impedance of the power source unit 3 is fixed.
Conventionally, therefore, the full-wave rectified output of the rectifier 3a is solely adjusted to a fixed voltage (Zener breakdown voltage) by using the Zener diode 3b, as shown in FIG. 6, and the full-wave rectified output is smoothed by means of a capacitor 3c to form a stable internal power source.
Although the internal voltage is regulated by means of the Zener diode 3b, however, the power energy supplied through the coil 2 inevitably considerably changes depending on the distance from the external apparatus. Accordingly, the MOS transistors that constitute the rectifier 3a must be ones having power capacity that ensures an allowance for the maximum power energy. Inevitably, therefore, the MOS transistors are increased in size (or increased in area). In the case where the information signals are modulated and transmitted or received with use of electromagnetic waves of a given frequency coupled to, for example, the coil 2 by electromagnetic induction as carriers, the regulation of the voltage by means of the Zener diode 3b may possibly ruin the resulting modulated components, depending on the extent of modulation.
The present invention has been contrived in consideration of these circumstances, and its object is to provide an electromagnetic-induction coupling device furnished with a power source circuit having a simple construction and capable of forming an internal power source from power energy supplied from an external apparatus by utilizing electromagnetic-induction coupling by means of a coil.
Another object of the present invention is to provide an electromagnetic-induction coupling device capable of realizing secure information communication such that its internal power source is formed steadily without regard to the change of power energy supplied from an external apparatus by utilizing electromagnetic-induction coupling by means of a coil in modulating information signals with use of the power energy as a carrier and transmitting and receiving the information signals.
In order to achieve the above objects, an electromagnetic-induction coupling device according to the present invention comprises a coil coupled to a magnetic field having power energy by electromagnetic induction, a rectifier for subjecting the power energy fetched by means of the coil to full-wave rectification, and a smoothing circuit for smoothing a rectified output from the rectifier and forming an internal power source. The device is particularly characterized by comprising an MOS transistor having a source and a drain individually connected across the coil and a constant-voltage control circuit capable of controlling the gate voltage of the MOS transistor in response to the output of the smoothing circuit, thereby limiting voltage (AC voltage) applied to the rectifier so that a rectified output voltage (DC voltage) obtained by means of the rectifier is fixed.
Thus, in the electromagnetic-induction coupling device according to the present invention, the MOS transistor is provided in parallel with the coil for fetching the power energy by electromagnetic-induction coupling, and the power energy is partially bypassed by means of the MOS transistor. The fixed DC voltage (internal power source) is obtained by thus limiting the power energy applied to the rectifier and the resulting AC voltage. If the gate voltage of the MOS transistor is controlled in accordance with the signal power source (DC voltage) that is obtained by smoothing the full-wave rectified output from the rectifier, in particular, some of the power energy can be alternatively bypassed in a manner such that the respective functions of the source and drain of the MOS transistor are changed depending on the polarity of the power energy (AC) obtained from the coil with respect to the gate voltage. In consequence, the power energy (AC) applied to the rectifier can be limited itself, so that the power capacity of a rectifier element (MOS transistor) that constitutes the rectifier can be reduced to match the power capacity required by its internal circuit, whereby the rectifier element (MOS transistor) can be downsized.
Further, an electromagnetic-induction coupling device according to the present invention comprises a data reception unit for detecting a modulated component of the power energy fetched by means of the coil and receiving an information signal represented by the modulated component and a data transmission unit for controlling the gate voltage of the MOS transistor in response to transmission information, changing the extent of electromagnetic-induction coupling to the magnetic field of the coil, and transmitting the transmission information.
In this electromagnetic-induction coupling device that further comprises the data reception unit and the data transmission unit, the MOS transistor is driven at the gate voltage that is generated in accordance with an internal voltage of which the high-frequency component is removed from the full-wave rectified output from the rectifier by means of the smoothing circuit. Accordingly, the power energy applied to the rectifier can be restrained without ruining the modulated component of the power energy obtained through the coil. In soothing the full-wave rectified output obtained from the rectifier to obtain the fixed internal voltage, therefore, the power energy applied to the rectifier is only limited by using the MOS transistor, as mentioned before. Thus, the modulated component that is obtained by modulating the information signal with use of the power energy fetched by means of the coil as the carrier can be detected securely.
Preferably, the rectifier is constructed by bridge-connecting four MOS transistors as rectifier elements and is integrated concurrently with the MOS transistors connected in parallel with the coil on a given semiconductor. The given semiconductor is realized as a ball semiconductor having the coil on its surface.